1. Field of the Invention
The present invention relates generally to tracking and updating bias in inertial sensor devices.
2. Related Art
Inertial measurement technology has been used since the 1920's in aviation with ballistics and space exploration applications following later in the twentieth century. Throughout this period, a solid knowledge base and sophisticated techniques for inertial measurement have been developed for applications where velocities and distances are measured using nautical miles or even astronomical units. Until recent years, applications better-suited to measurement using meters or millimeters generally did not utilize inertial measurement due to the prohibitive size, weight, and cost of the sensors. The introduction and steady improvement of sensors based on microelectromechanical systems (MEMS) and other small, less-expensive inertial sensors has opened the door to their use in such applications in the past decade.
Strap-down inertial measurement units developed from these new sensors offer several advantages over other position and velocity sensing strategies. Theoretically, acceleration, velocity, position, and orientation information may all be obtained from a single source. This reduces the number of sensors needed and the hardware complexity for the end user. The operation of inertial sensors is self-contained, reducing dependence on outside references, such as global positioning systems (GPS). MEMS inertial sensors are also extremely small and lightweight, with tri-axial accelerometers that occupy as little as 15 mm3 now being available.
Despite these advantages, applications of inertial sensors are still limited due to drawbacks that include bias drift, sensor accuracy, mounting, and calibration issues. Since velocity, position, and orientation are all derived through integration, the results of which are sensitive to all of these potential sources of error, they lead to unbounded error growth if outside references are unavailable.